I can't progress in the game. I've gotten to were I'm supposed to go to Millenium City but I can't get there at all. Syndey just says, "just that a stroll or something." The walkthrough says she is suppose to escort me to the city.

I have everything up on Youtube(last walkthrough link in OP).

OK I see what you did. Hmmm now lets see here. If you are wondering how to go there than you have to do some events first and then after them the scientist guy on Huntik Route will let you go through the cave he was previously was blocking. Through that cave you will reach trident waters. Surf south from there and you will reach Millenium city